U.S. Pat. No. 4,259,470 teaches a hot-melt, pressure-sensitive adhesive (HMPSA) comprising a propylene/1-butene or 1-pentene/higher alpha-olefin copolymer. The higher 1-olefin is hexene, heptane, octene, nonene, or decene and is present in the copolymers in 5 to 39 mole percent. The copolymer contains 10 to 55 mole percent propylene and 15 to 60 mole percent of either 1-butene or 1-pentene. No mention is made of ethylene in this patent.
U.S. Pat. No. 3,954,697 teaches a HMPSA comprising an amorphous propylene/higher 1-olefin copolymer containing 40 to 60 mole percent 1-olefin having a density of 0.85 to 0.86, a glass transition temperature of -30.degree. C. to -45.degree. C., and no measurable differential scanning calorimetry (DSC) melting point. Products from the teachings of this patent have a melt viscosity at 190.degree. C. of 10,000 to 75,000 centipoises (cp). All the products described are copolymers. The only monomers used are propylene and hexene-1 or higher 1-olefins.
None of the above-identified patents teach terpolymers containing ethylene. Prior art references that teach terpolymers containing ethylene do not teach polymers containing hexene (e.g., U.S. Pat. No. 4,415,718). The terpolymers of the present invention are useful as single component hot-melt, pressure-sensitive adhesives useful for tapes, labels, and the assembly of disposable items such as diapers, feminine hygenic napkins, surgical gowns, and surgical drapes.
The terpolymers of the present invention have properties which are particularly advantageous in view of prior art HMPSAs. For example, the terpolymers of this invention have a lower RBSP than the copolymers of the prior art and they can be used on heat-sensitive substrates such as polyethylene films without distorting the film. Therefore a lower application temperature can be used for the terpolymers which greatly expands the areas in which they can be used.
The terpolymers of this invention are also more economically desirable than certain prior art HMPSAs in that propylene is less expensive than 1-hexene.